Light pollution is increasing globally, in both developed and developing countries. Most of the data on the growth of light pollution comes from a handful of weather satellite images and computer modeling using population trends. An examination of North American light emissions shows a roughly six percent annual increase from 1947 to 2000 (Cinzano & Elvidge, 2003). This may be a conservative estimate, as measurements over smaller areas and shorter time spans show annual increases of eight percent for Las Vegas, Nevada (NPS measurements, 2002–2008), and 10 percent in northern Italy (Cinzano, 2000). These increases exceed the population growth rate, indicating that the increase in light pollution is primarily due to a multplication of two factors—more light emitted per capita and a greater percentage of uplight from light fixtures.
The exceptions to this rapid light pollution growth rate include Eastern Europe, which suffered economic hardship and government collapse in the 1990s, and areas where lighting regulations have been created and enforced, such as Tucson, Arizona, portions of Northern Italy (Falchi, 2011), and Flagstaff, Arizona (NPS measurements, 2002–2012).
Though the light pollution trend has been sobering and future predictions for dark skies are bleak, there are clear examples where efforts to protect and restore dark skies have been successful.
Cinzano, P., Elvidge C. 2003. Night sky brightness at sites from satellite data. Mem. Soc. Astron. It., 74, 456-457.
Unpublished NPS measurements based on 2002-2008 data.
Cinzano P. 2000. Measuring and Modeling Light Pollution. Mem. Soc. Astron. Ita., 71:1, 159-166.
Falchi F. 2011. Campaign of Sky Brightness and Extinction Measurements Using a Portable CCD Camera. Monthly Notices of the Royal Astronomical Society, Vol 412:1.
Unpublished NPS measurements based on 2002-2012 data.
For information on a 2016 study that shows the extent of light pollution across the night sky, read this press release.